Cleaning the surface of semiconductor substrates is a critical step in the integrated circuit fabrication process. Surface cleaning eliminates particulates and trace surface contaminations such as organic and metallic impurities. Traditionally, these cleaning techniques have been based almost entirely on chemical reagents, which selectively remove the surface contaminants and particulates without attacking or chemically altering the wafer surface. As the permissible concentrations of contaminants scale down with increasing device integration density, these traditional "wet" cleans are becoming increasingly supplanted by "dry" cleans which employ a vapor phase medium for the clean. Wet cleaning techniques also suffer from the limitation that liquid cleaning materials cannot penetrate the intricate topologies associated with the small geometries encountered in modern integrated circuits. Dry cleans also enjoy an advantage that they are compatible with the concept of integrated single wafer processing which emphasizes the need to isolate the wafer from an uncontrolled ambient during the fabrication sequence. In contrast, wet cleaning is performed at ambient pressure in an atmospheric environment. Contamination of the wafer surface is more likely in such an atmosphere. In addition, chemical waste generated by wet cleaning processes requires elaborate and expensive waste management.
Considerable progress has been made in developing dry or vapor phase cleans that are effective in removing some forms of contamination. In particular, vapor phase cleans are effective in the removal of native oxides and organic impurities. However, progress in the removal of metallic contaminants such as nickel, chromium, iron, zinc, and generic particulates has been more modest. Wet cleaning steps are usually used to remove these forms of contaminants.
Conventional wet cleaning systems use megasonic agitation in a solvent bath followed by rinsing and spin drying to remove particulates and contaminants from the wafer surface. Unless the particulates and contaminants can be volatilized, traditional vapor phase processing is incapable of removing the particulates and contaminants. Gas phase chemistries used to remove metallic contaminants must volatilize the impurities for effective removal. Halogen gases are effective in removing trace quantities of some metallic contaminants. O.sub.2 /O.sub.3 can remove some organic contaminants and HF/alcohols can remove native oxide. Nevertheless, there does not exist any cleaning process that combines the advantages of dry cleaning with the effectiveness of wet cleaning.